The proposed study is designed to elucidate some of the electrophysiological properties of smooth muscle cells from cerebral arteries. Parameters to be measured will include: membrane potential, action potential characteristics, time constants, space constants and contractions from large conductive and small resistive arteries. The changes which occur in the above mentioned parameters in response to neurotransmitters, metabolites, altered pH and gas tensions, and platelets will be determined. We will look for differences in the membrane electrical properties of vessels from different brain areas since it is known that certain substances (e.g., norepinephrine) effect contraction in the arteries of certain brain areas and not others. The voltage control of contraction will be determined by simultaneously measuring membrane potential and contraction from a given arterial strip. The ions which carry inward current during the action potential will be determined by ion substitution experiments. The voltage control over the channels which carry inward current will also be studied. The proposed study will reveal information concerning (1) basic electrophysiological properties of cerebral arterial smooth muscle, (2) the mechanism of action of neurotransmitters, metabolites and pH, and (3) the effect of platelets and substances released from them on the membrane electrical and mechanical properties of cerebral vascular muscle.